Premixer assembly and mechanism for altering natural frequency of a gas turbine combustor

ABSTRACT

A system and method are provided for altering the natural frequency of a dome plate portion of a premixer assembly of a gas turbine combustor. The plate assembly has a dome plate with a central pilot mixer and a plurality of extension tabs extending radially outward from the pilot mixer. A plurality of radially extending struts are secured to the extension tabs in order to alter the natural frequency of the dome plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/815,835, filed on Apr. 25, 2013. This application is related by subject matter to commonly-assigned U.S. Non-Provisional Patent Applications entitled REMOVABLE SWIRLER ASSEMBLY FOR A COMBUSTION LINER (Attorney Docket No. PSM-316/PSSF.199280) and PREMIXER ASSEMBLY FOR A GAS TURBINE COMBUSTOR (Attorney Docket No. PSM-317/PSSF.199281).

TECHNICAL FIELD

The present invention generally relates to a gas turbine combustor. More specifically, embodiments of the present invention relate to an apparatus and method for altering the natural frequencies of the dome plate assembly for a gas turbine combustor.

BACKGROUND OF THE INVENTION

In a typical gas turbine engine, a compressor having alternating stages of rotating and stationary airfoils is coupled to a turbine through an axial shaft, with the turbine also having alternating stages of rotating and stationary airfoils. The compressor stages decrease in size in order to compress the air passing therethrough. The compressed air is then supplied to one or more combustors, which mixes the air with fuel. An ignition source proximate the one or more combustors ignite the mixture, forming hot combustion gases. The expansion of the hot combustion gases drives the stages of a turbine, which is coupled to the compressor through an axial shaft. The exhaust gases can then be used as a source of propulsion, to generate steam through a heat recovery steam generator, or in powerplant operations to turn a shaft coupled to a generator for producing electricity.

The combustion system of a gas turbine engine can take on a variety of configurations. A combustion system for a gas turbine engine can comprise a single combustion chamber, a plurality of individual combustion chambers spaced about the axis of the engine, a plenum-type combustion system, or a variety of other combustion systems. Depending on the engine geometry, performance requirements, and physical operating location, the exact combustor arrangement will vary.

A typical combustion system generally comprises at least a casing secured to the frame of the engine, a combustion liner secured within at least a part of the casing, and one or more fuel nozzles positioned within or adjacent to the combustion liner for injecting a fuel (gas, liquid, or both) into the combustion chamber. The combustion system is in fluid communication with the engine. More specifically, the casing and liner arrangement provides a way for air from the compressor to enter the combustion system, where it mixes with fuel from the one or more fuel nozzles. The fuel-air mixture is ignited by an ignition source, such as a spark igniter. Hot combustion gases travel through the combustion liner and often through one or more transition pieces and into the turbine. The transition piece is essentially a duct having a geometry that changes from the shape of the combustor to the inlet of the turbine.

The combustion liner is at the center of combustor operations. The combustion liner geometry is dictated by the operating parameters of the engine, performance requirements, or available geometry. While combustion liner geometries can vary, the combustion liner typically includes at least a portion for receiving fuel nozzles, for mixing fuel and air together and for containing the reaction when the fuel and air mixture is ignited.

Combustion liners of the prior art have met certain performance requirements, but have also exhibited various shortcomings. Combustion liners are subjected to various thermal conditions and as such must be able to withstand the high thermal and mechanical stresses of such operating conditions. By nature, the combustion liner has a series of natural operating frequencies. The gas turbine engine and combustion system also have a natural frequency, and orders of the natural frequency (i.e. 1E, 2E, 3E, etc.). When a component, such as the combustion liner, has a natural frequency or mode that coincides with, or approaches, an engine natural frequency or order thereof, the component can become dynamically excited. If care is not taken to avoid the crossings of these frequencies, operating at these frequencies, or minimizing the time for the crossing, the component may experience excessive wear or failure as a result of the vibratory stress that occurs when operating at or near the natural frequency of the gas turbine engine or combustion system.

SUMMARY

In accordance with the present invention, there is provided a novel and improved component for a combustion liner of a gas turbine engine. The combustion liner is generally cylindrical in shape and has an inlet end and a discharge end, opposite the inlet end. The combustion liner of the present invention comprises a premixer assembly capable of receiving a plurality of fuel nozzles. The premixer assembly is designed so as to provide a way of altering its natural frequency.

In accordance with an embodiment of the present invention, there is provided a plate assembly for a gas turbine combustor, the plate assembly comprising a dome plate, a pilot mixer assembly, a plurality of extension tabs extending from an outer wall of the pilot mixer assembly, and a plurality of radially extending struts secured to both the extension tabs and the dome plate.

In accordance with another embodiment of the present invention, a system is provided for altering the natural frequency of a premixer assembly. The system comprises a generally circular dome plate, a pilot mixer having an outer wall portion, a plurality of extension tabs fixed at one end to the outer wall and extending through a pilot cone portion, and a plurality of struts extending between the extension tabs and the dome plate.

In accordance with yet another embodiment of the present invention, a method of altering the natural frequency of a premixer assembly is provided. The method comprises the steps of providing a dome plate, a pilot mixer assembly, a plurality of extension tabs, and a quantity of radially extending struts. The quantity of radially extending struts are secured to the plurality of extension tabs and dome plate. Then, additional radially extending struts are secured to the plurality of extension tabs and dome plate upon a determination to increase stiffness of the dome plate. Altering the stiffness of the dome plate in turn alters its natural frequency such that its natural frequency is outside of the dynamic frequencies generated by the combustion system.

Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The instant invention will now be described with particular reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 is a partial cross section view of a gas turbine engine of the prior art in which a combustion system in accordance with an embodiment of the present invention is capable of being used;

FIG. 2 is a cross section view of a gas turbine combustor of the prior art capable of operating within the gas turbine engine of FIG. 1;

FIG. 3 is a perspective view of a combustion liner incorporating an embodiment of the present invention;

FIG. 4 is a cross section view of the combustion liner of FIG. 3 taken through a pilot mixer assembly in accordance with an embodiment of the present invention;

FIG. 5 is an alternate view of the cross section of FIG. 4, in accordance with an embodiment of the present invention;

FIG. 6 is a cross section view of a combustion liner of FIG. 3 taken through the a swirler assembly and pilot mixer assembly in accordance with an embodiment of the present invention;

FIG. 7 is an alternate view of the cross section of FIG. 6, in accordance with an embodiment of the present invention;

FIG. 8 is a detailed cross section view taken through the inlet portion of the combustion liner of FIG. 3 in accordance with an embodiment of the present invention;

FIG. 9 is a partial cross section view of the main swirler portion of the combustion liner in accordance with an embodiment of the present invention;

FIG. 10 is a perspective view of a pilot mixer assembly in accordance with an embodiment of the present invention;

FIG. 11 is cross section view of a portion of the pilot mixer assembly of FIG. 10 in accordance with an embodiment of the present invention;

FIG. 12 is a perspective view of a plate assembly of a gas turbine combustor in accordance with an embodiment of the present invention;

FIG. 13 is cross section view of the plate assembly of FIG. 12 in accordance with an embodiment of the present invention;

FIG. 14 is an alternate cross section view of the plate assembly of FIG. 12 in accordance with an embodiment of the present invention; and,

FIG. 15 is a flow diagram describing a method of altering the natural frequency of a premixer assembly in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different components, combinations of components, steps, or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies.

Referring initially to FIG. 1, a gas turbine engine 100 of the prior art in which the present invention can be used is disclosed. The gas turbine engine 100 generally comprises an outer casing 102, enveloping the main portions of the engine. A shaft 104 extends axially along engine axis A-A and couples a compressor 106 to a turbine 108. The compressor 106 receives air through inlet region 110 and directs the air through alternating rows of rotating and stationary airfoils of decreasing size in order to compress the air passing therethrough, thereby increasing air temperature and pressure. The compressed air is then directed through one or more combustion systems 112 where fuel and air are mixed together and ignited to form hot combustion gases. The hot combustion gases are then directed into the turbine 108 to pass through alternating rows of rotating and stationary airfoils of increasing size so as to expand the fluid and harness the energy from the combustion gases into mechanical work to drive the shaft 104. The shaft 104 may also be coupled to a shaft of an electrical generator (not shown) for purposes of generating electricity.

FIG. 2 discloses a cross section of a combustor 200 of a gas turbine engine of the prior art. As such, this typical gas turbine combustor 200 comprises a casing 202, a cover 204, one or more fuel injectors 206, and a combustion liner 208. A transition piece 210 connects the combustion liner 208 to an inlet of the turbine 212.

The present invention is shown in detail in FIGS. 3-15 and discloses a new and improved system and method for altering the natural frequency of a dome plate in a gas turbine combustor. Referring initially to FIGS. 3-7, a combustion liner 300, in which the present invention operates, is disclosed and comprises a plate assembly 430. The plate assembly 430 is part of a larger premixer assembly 330 and is shown in more detail in FIGS. 12-14. The plate assembly 430 generally comprises a dome plate 334 having a central opening 432 contained therein, the central opening 432 passing through the thickness of the dome plate 334. The dome plate 334 also comprises a plurality of openings 370 arranged in an annular array about the central opening 432. The plurality of openings 370 are sized to contain swirler assemblies 332 for the premixer 330. However, for clarity, the swirler assemblies 332 have been removed from FIGS. 12-14. The plurality of swirler assemblies 332 are oriented about the axis of the combustion liner and secured to a dome plate 334. The main swirler assemblies 332, shown in more detail in cross section in FIG. 8, comprise a swirler body 336 comprising a plurality of turning vanes 338 secured to a center ring 340 and an outer sleeve 342. The turning vanes 338 impart a swirl to a passing flow. Secured to the outer sleeve 342 is a forward mounting block 344 and an aft mounting block 346. The forward mounting block 344, aft mounting block 346, and fasteners 350 and 358 are used to secure the swirler assemblies 332 to the combustion liner 300.

The dome plate 334 further comprises a plurality of openings, or air holes, 374 extending through the thickness of the dome plate 334. For the embodiment depicted in FIGS. 9 and 12-14, the cooling holes 374 are oriented generally perpendicular to the dome plate 334. Alternatively, the cooling holes 374 could be oriented at a surface angle relative to the dome plate 334 as well as a compound angle. The dome plate 334 includes numerous cooling holes 374 for directing a flow of compressed air into the combustion zone of the combustion liner 300. The exact quantity, size, and shape of the cooling holes 374 can vary depending on the amount of compressed air to be directed through the dome plate 334 as well as to maintain a desired pressure drop into the combustion zone. For the dome plate depicted in FIGS. 12-14, the cooling holes 374 are approximately 0.165″ in diameter and the dome plate 334 includes over 200 cooling holes. The exact size, quantity, and spacing of the cooling holes 374 in the dome plate 334 can vary depending on factors such as the amount of air to pass through the dome plate as well as the desired drop in pressure across the dome plate.

The swirler assemblies 332 are positioned so as to be in fluid communication with adjacent tubes 352, or hoovers, which pass the flow of fuel and air from the swirler assembly 332 to the mixing zone of the combustion liner 300. That is, the swirler assemblies 332 are positioned so as to be adjacent to or slightly engaged in the tubes 352.

The plate assembly 430 also comprises a pilot mixer assembly 440. The pilot mixer assembly 440, while shown in the plate assembly 430 in FIGS. 12-14, is shown in detail in FIGS. 10 and 11. The pilot mixer assembly 440 extends from the central opening 370 and has an outer wall 442, a center ring 444 located within the outer wall 442. Extending between the center ring 444 and the outer wall 442 are a plurality of swirler vanes 446. Located around a portion of the outer wall 442 is a pilot cone 448. The pilot cone 448 is positioned radially outward of the outer wall 442, and tapers radially inward towards the central opening 370. The pilot cone 448 then extends through the dome plate 334 and transitions into a divergent portion 448A.

The plate assembly 430 also comprises a plurality of extension tabs 450 extending from the outer wall of the pilot mixer assembly 440 and through the pilot cone 448. The plurality of extending tabs 450 are secured to the outer wall 442 of the pilot mixer assembly 440. The plurality of extending tabs can be secured to the outer wall 442 via a weld, braze or other acceptable joining process. Alternatively, the plurality of extending tabs 450 can be integrally formed with the outer wall 442 of the pilot mixer assembly 440, as would be produced via a casting process.

The plate assembly 430 also comprises a plurality of radially extending struts 452 secured to the plurality of extension tabs 450. The plurality of struts 452, or stiffeners, are used to provide increased rigidity and support to the dome plate 334, thereby increasing the stiffness of the plate assembly 430, resulting in an increase in its natural frequency. The struts 452 are oriented generally perpendicular to the dome plate 334 and are secured at one end to the plurality of extension tabs 450 and at an opposing end to the dome plate 334, as shown in FIGS. 12 and 13. More specifically, the radially extending struts 452 are secured to the extension tabs 450 and the dome plate 334 by a weld, braze or other acceptable securing means. As shown in FIGS. 12 and 13, the radially extending struts 452 are positioned between adjacent plurality of openings 370. For the embodiment depicted in FIGS. 13 and 15, four struts 394 are used. However, the number of struts could be increased to equal the number of main swirler assemblies 332, which in an embodiment of the present invention is eight.

The radially extending struts 452 are secured to the dome plate 334 at multiple locations, as shown in FIGS. 12 and 13. For example, the radially extending struts 452 are secured at a location radially inward, towards the central opening 370 and radially outward towards an outer edge of the dome plate 334. That is, the radially extending struts 452 have an interrupted surface 452A that is spaced a distance from the dome plate 334 in multiple locations.

The radially extending strut and extension tab configuration described herein is merely one such embodiment of a configuration to adjust the natural frequency of the dome plate 334. The design described herein, where the extension tab 450 is secured to the radially extending strut 452, is one such embodiment that lends to ease of manufacturing, lower manufacturing costs, while providing a design that alters the natural frequency of the dome plate. It is conceivable that other configurations for the radially extending strut and extension tabs are possible.

The present invention also provides a system for altering the natural frequency of a premixer assembly, where the system comprises a generally circular dome plate 334 having a central opening 432, an upstream face 334A, an opposing downstream face 334B, and a plurality of cooling holes 374. A pilot mixer assembly 440 is located within the central opening 432 where the pilot mixer assembly 440 has an outer wall 442 and a pilot cone 448 that surrounds a portion of the outer wall 442, as shown in FIGS. 10 and 11. The system for stiffening the premixer assembly also comprises a plurality of extension tabs 450 extending from the outer wall 442 of the pilot mixer assembly 440 and through the pilot cone 448. A plurality of struts 452 extend between the plurality of extension tabs 450 and the dome plate 334, as shown in FIGS. 12 and 13. More specifically, for the embodiment of the present invention shown in FIGS. 12 and 13, the struts 452 extend radially outward from some of the plurality of extension tabs 450 and are positioned in a way to provide a desired natural frequency to the generally circular plate assembly 430.

As discussed above, and shown clearly in FIGS. 12 and 13, the plurality of struts 452 comprise an interrupted or recessed portion 452A located between regions where the struts are in contact and secured to the dome plate 334. This recessed portion 452A provides a way by which cooling air can pass between adjacent swirler assemblies 332 in order to cool that portion of the dome plate 334. In fact, to further aid in the cooling of the dome plate 334, the dome plate 334 includes multiple cooling holes 374 positioned under the recessed portion 452A of the struts 452.

Referring to FIGS. 13 and 14, the system for stiffening the premixer assembly also comprises an outer cone 460 that envelopes a portion of the pilot cone 448, and more specifically, the outer cone 460 envelopes the divergent portion 448A of the pilot cone 448. The outer cone 460 is spaced a distance from the pilot cone 448 so as to maintain a flow of cooling air between the outer cone 460 and the pilot cone 448 for cooling the pilot cone 448, including the divergent portion 448A. The gap between divergent portion 448A and outer cone 460 can vary depending on operating conditions, but for the embodiment depicted in FIGS. 13 and 14, is approximately 0.055 inches. The gap is maintained by way of dimpled portions in the outer cone 460 causing local contact with regions of the pilot cone 448 when the combustor is operating. In a non-operation, cold state, the dimpled portions in the outer cone 460 do not contact the pilot cone 448. In prior diffuser/pilot cone configurations an outer cone similar to that disclosed herein was welded to a pilot cone causing the welded assembly to be overly constrained, resulting in high mechanical stresses and resulting in component cracking and failure.

Referring now to FIG. 15, the present invention also comprises a method 500 of altering natural frequency of a premixer assembly. Specifically, in a step 502, a dome plate and pilot mixer assembly are provided where the pilot mixer assembly has a plurality of extension tabs. In a step 504, a quantity of radially extending struts are secured to a plurality of extension tabs. Depending on the desired natural frequency of the dome plate, in a step 506, additional radially extending tabs are secured to the dome plate and to additional extension tabs in order to increase the natural frequency of the dome plate. Alternatively, in order to decrease the natural frequency of the dome plate, one or more radially extending struts can be removed from the premixer assembly.

The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments and required operations, such as machining of shroud faces other than the hardface surfaces and operation-induced wear of the hardfaces, will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope.

From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims. 

1. A plate assembly for a gas turbine combustor comprising: a dome plate having a central opening therein and a plurality of openings arranged in an annular array about the central opening; a pilot mixer assembly extending from the central opening, the pilot mixer assembly having an outer wall, a center ring located within the outer wall, a plurality of pilot vane swirler vanes extending therebetween, and a pilot cone surrounding a portion of the outer wall; a plurality of extension tabs extending from the outer wall of the pilot mixer assembly and through the pilot cone; and, a plurality of radially extending struts secured to the plurality of extension tabs and the dome plate.
 2. The plate assembly of claim 1, wherein the plurality of openings in the dome plate are each sized to receive a swirler assembly.
 3. The plate assembly of claim 2 further comprising a plurality of swirler assemblies, each comprising a premix tube, a premix swirler positioned within the premix tube, the swirler having a plurality of turning vanes for imparting a swirl to a passing flow, and a plurality of mounting of mounting blocks positioned on the outer wall of the premix tube;
 4. The plate assembly of claim 1, wherein the dome plate further comprises a plurality of air holes extending through the dome plate.
 5. The plate assembly of claim 1, wherein the plurality of extending tabs are secured to the outer wall of the pilot mixer assembly.
 6. The plate assembly of claim 1, wherein the pilot cone extends through the dome plate and transitions into a divergent portion.
 7. The plate assembly of claim 4, wherein the radially extending struts have an interrupted surface in contact with the dome plate such that each of the struts are secured to the dome plate at multiple locations.
 8. The plate assembly of claim 1, wherein the radially extending struts are positioned between adjacent plurality of openings.
 9. A system for stiffening a premixer assembly comprising: a generally circular dome plate having a central opening, an upstream face, an opposing downstream face, and a plurality of cooling holes; a pilot mixer assembly located within the central opening, the pilot mixer assembly having an outer wall and a pilot cone surrounding a portion of the outer wall; a plurality of extension tabs extending from the outer wall of the pilot mixer assembly and through the pilot cone; and, a plurality of struts extending between the plurality of extension tabs and the dome plate and radially outward from the outer wall of the pilot mixer assembly, the plurality of struts being fewer than the plurality of extension tabs; wherein the plurality of struts are positioned about the pilot mixer assembly in order to provide a desired natural frequency to the generally circular dome plate.
 10. The system of claim 9, wherein the generally circular dome plate further comprises a plurality of swirler assemblies oriented in an annular array about the pilot mixer assembly.
 11. The system of claim 9, wherein the plurality of extension tabs are welded to both the outer wall and the plurality of struts.
 12. The system of claim 11, wherein each of the plurality of struts are secured to the dome plate at multiple locations.
 13. The system of claim 12, wherein each of the plurality of struts, further comprise a recessed portion between the multiple locations where the plurality of support plates are secured to the dome plate.
 14. The system of claim 1, wherein the plurality of struts are positioned in between the plurality of openings in the dome plate.
 15. The system of claim 1, wherein the pilot cone has a diffuser section extending from proximate the downstream face of the dome plate.
 16. The system of claim 15 further comprising an outer cone enveloping a portion of the pilot cone, the outer cone spaced a distance from the pilot cone so as to maintain a gap therebetween.
 17. A method of altering natural frequency of a premixer assembly comprising: providing a dome plate having a central opening therein and a plurality of openings arranged in an annular array about the central opening, a pilot mixer assembly located within the central opening and having an outer wall, and a pilot cone surrounding a portion of the outer wall, and a plurality of extension tabs extending from the outer wall of the premixer and through the pilot cone; securing the quantity of radially extending struts to the plurality of extension tabs and the dome plate; and, securing additional radially extending struts to the plurality of extension tabs and the dome plate upon a determination to increase the natural frequency of the dome plate.
 18. The method of claim 17, wherein the quantity of radially extending struts equals the plurality of openings arranged in an annular array about the central opening.
 19. The method of claim 17, wherein the natural frequency of the premixer assembly is increased upon securing additional radially extending struts to the plurality of extension tabs and the dome plate.
 20. The method of claim 17, wherein the natural frequency of the premixer assembly is decreased by removing radially extending struts from the premixer assembly such that the struts do not contact the plurality of extension tabs and the dome plate. 